Tuning indicator circuits



Nov. 30, 1937.

R. H. SIEMENS TUNING INDICATOR CIRCUITS Filed Aug. 26, 1936 INVENTOR RUDOLPH H. SIEMENS ATTORNEY Patented Nov. 30, 1937 TUNING INDICATOR CIRCUITS Rudolph H. Siemens, Richmond Hill, N. Y., assignor, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application August 26, 1936, Serial No. 98,006

6 Claims.

My invention relates to circuits for converting high frequency alternating currents into low frequency and direct currents, and more particularly to radio circuits incorporating visual voltage or tuning indicators of the electron discharge type.

One embodiment of such a device useful as a tuning indicator and described in Patent 2,051,189 allowed August 18, 1936 to Herbert M. Wagner and assigned to the Radio Corporation of America, comprises an envelope having within it a straight thermionic equipotential cathode provided with two separate emitting sections, one of which is surrounded by amplifier elements which may comprise a control grid and anode, and the other of which is surrounded by the tuning indicator elements of the tube consisting of a straight control electrode parallel to the cathode and an anode or target coated with fluorescent material which may be concentric with and surrounding the cathode and the control electrode. In operation electrons flow from the cathode to the fluorescent anode with sufiicient velocity to bombard the fluorescent anode and render it luminous. The control electrode is connected to the amplifier anode and the tube so connected into a radio receiving circuit that when the circuit is tuned to resonance with an incoming signal the luminous portion of the plate is of a predetermined width. The device is to advantage so connected that when the circuit is tuned to resonance the luminous portion of the anode of the tuningindicator portion is of maximum width and the dark portion of minimum width, preferably the entire anode becoming fluorescent and the dark portion disappearing.

In one of the conventional circuits in which the above tuning indicator tube is used, the intermediate or radio frequency amplifier of the radio receiver is coupled to a thermionic diode rectifier having in its output a resistor across which a direct voltage is developed and which is applied as a grid bias voltage to the intermediate frequency or radio frequency amplifier to obtain an automatic volume control action, and also to the audio amplifier. The grid of the tuning indicator above described may also be connected to the same point in the output of the rectifier, and the indicator responds to this bias voltage to visually indicate the amplitude of the rectified voltages impressed on the rectifier by the preceding amplifier stages. Maximum voltage is indicated when the receiving circuit is tuned to resonance. In some cases a separate rectifier is used solely for the purpose of providing a direct voltage bias for the tuning indicator tube. In either case it is necessary to employ a stage of rectification before the tuning indicator.

It is the object of my invention to provide a circuit arrangement making use of the above described tuning indicator tube as a combined visual tuning or voltage indicator, detector or rectifier and automatic volume control device.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawing in which the single figure of the drawing is a diagrammatic repre-' sentation of a radio receiving circuit embodying my invention.

Briefly the signal received is fed to an amplifier which is coupled to the combined tuning indicator, detector or rectifier and automatic volume control device by connecting in accordance with my invention the output of the amplifier between the grid and cathode of the tuning indicator tube. Rectification is accomplished by these two electrodes. The output of the tuning indicator tube is coupled to the amplifier to control its gain and to the audio frequency amplifier, proper filtering arrangements being used. By suitable circuit arrangement the indicator tube develops its own bias which is applied to the grid to cause indication of the amplitude of the rectified voltage and hence resonance conditions and filtering arrangements are also provided to insure proper operation of the tuning indicator portion of the tube.

Referring to the drawing, the signal received by the antenna I0 is impressed on the amplifier H, the output of which is coupled to the tuning indicator tube by means of a tuned circuit comprising the secondary of the transformer I2 and the con- 4 denser l3.

The thermionic voltage or tuning indicator has an envelope I4 containing a two-section cathode l5, the amplifier portion of the tube comprising grid l1 and anode l8 surrounding one section of 45 the cathode and the visual indicating portion surrounding the other portion of the cathode and comprising an anode l9 which fiuoresces during operation, and a control eelctrode 20 electrically connected to the anode I8 for determining the portion of the fluorescent anode upon which the electrons from the cathode strike to cause it to fiuoresce, the shadow caused by the control rod on the anode depending upon the difierence in Voltage between the control electrode 20 and the anode l9. Resistor H is connected between the,

. anode I8 and. the anode I9 for developing a difier- I ence in potential hetweenthe anode I9 and el-ec-w trode 20'during'operation of the tube when cur- I rent flows in the anode of the tube. a

In accordance with. my invention the tuned circuit comprising the secondary of'transformer l2, and condenser I3 is connected between cathode I5 and grid ll of the indicator tube l4, resistor 2-2 and condenser 23 being connected ;in ,seriesivwiththe tuned circuit and theindicator tube: Rectified voltage comprising'tan audio .fre-

quency component and a. more or lessrsteady direct voltage component appears across the im- I I on the rectifier circuit by amplifier I I are rectified,

.the condenser'23 being charged to peak rectified t e which appear across the resistor 22 Rectification and detection therefore takes place I between grid I- 'Iand cathode I501" indicator tube. I

to control its gain through the filter comprising resistor 24 and condenser 25 which filters out 'the I audio frequency voltages appearing across re- The I audio frequency voltages are ap- I I plied through a coupling condenser 26 to audio sistor 22.

frequency amplifier 27 the output. of whichis I connected to a translating device such as loud-' speaker 28-. The voltage drop across resistor 22 is also applied :to thegrid ;I'I of the tube QM and thus makes the tube self biasing. This action is made use of in the indicator portion of the tube as willbe, described below.

In operation the signals received by antenna 1 are amplified and impressed uponthe tuned circuit comprising secondaryoftrans'former I2 and I condenser I3, rectification taking place between the grid I I and cathode I 5, the direct voltage and audio voltage appearing across resistorr22 and condenser 23 and used for automatic volume control andto excite the audio amplifien-as above described. The bias developed across this resistor is applied to grid I'I so that the visual indicating tube acts as a self biaseddevice. The degree of biasdeveloped across resistor 22 and hence on the grid I' I determines the currentfiowing to the anode I8 and hence'the-drop through resistor} I. Withtheset detuned very littleor no voltage drop'appearsacross resistor 22; Under these conditions cathode I and grid I! are at subsignal rectified current flows through resistor 22 developing a voltage drop across resistor 22. This appears as a negative bias on the grid I1 and reduces the current flowing in the anode I8 and hence the drop through' resistor 2I. The potential difference therefore between the control electrode connected to anode I8 and the fluorescent anode is reduced'permitting more of the fluorescent anode-to be struck by electrons from the This bias voltage appearing at the tuned circuit I end of: resistor: 22 is applied to the amplifier: II I cathode I5 to cause the anodeto fiuoresce. The constants of the circuit can be so chosen that .substantiallythe entire anode fiuoresces when the Inasmuch as the set is tuned to resonance' audio frequency voltage appears across resistor 22 and hence on grid M, if this voltage is not bypassed and ispermitted to appear across resistor 2| the result wouldbe a fluctuation of the pattern i on the fiuorescent anode. Therefore, the condenser 29 is provided between cathode I5 I and anode I8 to by-pass' these'voltages back to the cathode so that only a steady voltage drop appears across resistor 21. .I I

It will thus be seen that by the novel circuit I which I have provided I eliminate the need for a separatediode rectifier and provide. a self-biased I visual tuning indicator device which also provides fier, the tube alsovisually indicating the amplimerits of my invention of which I now aware 'and ha've also indicated only'one specific applica .tion forwhich my invention may be employed,

rectification .for the automatic volume control I I bias anddeteetion for :th'eaudio frequency'ampli- I I I I 20 .tude of the rectified radio frequency or intermedig I ate frequency voltages as the set is tuned to resonance. I I I I it will'be apparent that myinvention' is by no means limited-to thefexactforms illustrated or 30 befmade mine: particular structure usedand the I I I.

I purpose for which it is employed without depart- I I I ing from the scope of my inventionas set forth the use indicated, but that many variations may in the aphendedcjlaims; I I I "WhatIclaim as'new isz' 1. Acircuit for rectifying alternating currents and visually indicating the amplitude of'the recti: I I fied currents and resulting" voltages andinclud I i inga thermionic device having a cathode, a grid' land anode surrounding one portioncfthe cathode and a fiuorescent anode and control electrode adjacent another portion of the cathode, said control electrode'being electrically connected tothe first anode, means for impressing alternating voltages upon said thermionic device, said means including a circuit connected between the grid and cathode of said thermionic device forrecti- V fying alternating currents and producing rectified voltages anda condenser connected between the first anode and cathode of said thermionic device. I

2. A circuit fo-rrectifying alternating currents and visually indicating the amplitude'of the rectified currents and resulting voltages, and including a thermionic device havinga cathode, a grid and anode surrounding a portion of the cathode, and a fluorescent anode and control electrode adjacent another portion of the cathode, said control electrode being connected to the first anode, anamplifier upon which is impressedan alternating voltage, an output for saidramplifier and means for coupling the output of said amplifier to said thermionic device, and including a circuit having an impedance therein and connectedbetween the grid and cathode of said thermionic device for rectifying amplified alternating currents and producing rectified voltages, said rectified voltages appearing across said impedance, and a condenser connected between the first anode and said cathode.

3. A circuit for rectifying alternating currents and visually indicating the amplitude of the rectified currents and resulting voltages, and including a thermionic device having a cathode, a grid and anode surrounding a portion of the cathode,

and a fluorescent anode and control electrode adjacent another portion of the cathode, said control electrode being connected to the first anode, an amplifier upon which is impressed an alternating voltage, an output for said amplifier and means for coupling the output of said amplifier to said thermionic device, and. including a circuit having an impedance therein and connected between the grid and cathode of said thermionic device for rectifying amplified alternating currents and producing rectified voltages, said rectified voltages appearing across said impedance, a condenser connected between the first anode and said cathode and a resistor connected between the first anode and said fluorescent anode.

4. A circuit for amplifying and rectifying alternating currents and visually indicating the amplitude of the rectified currents and resulting voltages, and including a thermionic device having a cathode, a grid and anode surrounding a portion of the cathode, and a fluorescent anode and a control electrode adjacent another portion of the cathode, said control electrode being connected to the first anode, an amplifier upon which is impressed an alternating voltage, an output for said amplifier and means for coupling the output of said amplifier to said thermionic device, and including a circuit having a resistor therein and connected between the grid and cathode of said thermionic device for rectifying the amplified alternating currents and providing rectified voltages, said rectified voltages appearing across said resistor, a condenser connected between the first anode and said cathode and a resistor connected between the first anode and said fluorescent anode, and means connected to the first resistor and the amplifier for controlling the gain in said amplifier.

5. A radio circuit for a combined visual tuning indicator, detector and automatic volume control device and including an amplifier upon which radio frequency voltages are impressed and an electron discharge device including a cathode and a grid and anode surrounding a portion of the cathode and a visual tuning indicating section comprising a fluorescent anode surrounding another portion of said cathode and a control electrode positioned between said fluorescent anode and the cathode and connected to the first anode, a circuit connected between said grid and cathode and coupled to said amplifier for rectifying the voltages impressed on said amplifier and a resistor in said circuit across which the rectified voltages appear, and a connection between said resistor and said amplifier for controlling the gain of said amplifier, and a condenser connected between the anode and cathode of said electron discharge device.

6. A radio circuit for a combined visual tuning indicator, detector and an automatic volume control device including an amplifier upon which radio frequency voltages are impressed, an electron discharge device comprising a cathode, a grid and an anode surrounding one portion of said cathode and a fluorescent anode adjacent another portion of the cathode, a control electrode between said fluorescent anode and said cathode and electrically connected to the first anode and a resistor connected between the first anode and the fluorescent anode, and a circuit including a resistor connected between the grid and cathode of said electron discharge device for rectifying the amplified voltages from said amplifier, said rectified voltages appearing across said resistor, a connection between said resistor and said amplifier for controlling the gain of said amplifier, an audio frequency amplifier and means for coupling said audio frequency amplifier to the circuit connected between the grid and cathode of said electron discharge device and a condenser connected between the first anode and cathode of said electron discharge device.

RUDOLPH H. SIEMENS. 

